The invention relates to a steering column for a motor vehicle, which comprises a jacket unit supporting a steering shaft rotatably about its longitudinal axis and a retaining part, which the jacket unit is secured non displaceably up to a limit value of a force acting onto the jacket unit parallel to the longitudinal axis of the steering shaft in the direction toward the front of the motor vehicle. If the limit value is exceeded, the jacket unit is displaceable parallel to the longitudinal axis in the direction toward the motor vehicle front. The jacket unit is connected with the retaining part, for one, across an energy absorption connection, which comprises at least one bending wire or strip that, upon a displacement of the jacket unit with respect to the retaining part parallel to the longitudinal direction toward the motor vehicle front, is deformed, and is connected, for another, across a break-away connection which, up to the limit value of the force, is closed and blocks a displacement of the jacket unit with respect to the retaining part and which is released if the limit value of the force is exceeded. The invention further relates to a method for the production of such a steering column.
Steering columns for motor vehicles are most often implemented such that they are adjustable so that the position of the steering wheel can be adapted to the seating position of the driver. Such adjustable steering columns are known in various embodiment forms. Apart from adjustable steering columns which are only adjustable in the length or height or inclination direction, steering columns are also known which are adjustable in the length as well as also the height or inclination direction.
As a safety measure in the event of a vehicle crash, it is known and conventional to realize in steering columns for motor vehicles the steering shaft together with a jacket unit, rotatably supporting the steering shaft, in a section adjoining the steering wheel-side end such that it is displaceable in the longitudinal direction of the steering column (=parallel to the longitudinal axis of the steering shaft) with the absorption of energy. A conventional implementation form provides for this purpose that a bracket unit, with respect to which in the opened state of the clamping mechanism the jacket unit is displaceable for setting the position of the steering column, is so connected with a mounting part attached on the vehicle chassis that the jacket unit with the absorption of energy is dislocatable with respect to the mounting part. Such a construction is shown, for example, in U.S. Pat. No. 5,517,877 A.
DE 28 21 707 A1 discloses a non-adjustable steering column in which the jacket tube rotatably supporting the steering shaft includes bilaterally projecting fins which had been connected on the chassis by securement blocks and bolts penetrating therethrough. In the event of a crash, the fins can become detached from the securement blocks, whereby a dislocation of the jacket tube is enabled. Between the securement blocks and the fins, U-shaped bending strips are herein provided on which deformation work is carried out during the dislocation of the jacket tube. The bending strips are enclosed in chambers of the fins and are in contact on opposing side walls of the chambers such that the rolling radius of the particular bending strip during its deformation is limited and predetermined.
An adjustable steering column comprising a jacket unit rotatably supporting the steering shaft and a bracket unit, with respect to which the jacket unit in the opened state of a securement device is displaceable for setting the position of the steering column at least in the longitudinal direction of the steering column, is disclosed in EP 0 598 857 B1. In the event of a crash, the jacket unit can be dislocated with respect to the bracket unit or with respect to a clamp bolt of the securement device in the longitudinal direction of the steering column. For the energy absorption, bending strips or bending wires are provided that are entrained with the jacket unit and placed about the clamp bolt, which strips or wires are deformed. One disadvantage of this solution is that the possible displacement path or the characteristic of the energy absorption in this device depends on the particular positioning length of the steering column.
Further, U.S. Pat. No. 5,961,146 A describes a steering column which in normal operation is only adjustable in the height direction. In a manner similar to that described above, a bending wire is provided curved in the shape of a U about the clamp bolt of the securement device, which in the event of a crash is entrained by the jacket unit dislocating with respect to the clamp bolt in the longitudinal direction of the steering column, whereby bending work is performed.
In the steering column disclosed in WO 2007/048153 A2, in the closed state of the securement device a retaining part is prevented by a securement part of the securement device from being displaced with respect to this securement part referred to the direction parallel to the steering shaft. The jacket unit can become dislocated in the longitudinal direction of the steering column with respect to the retaining part with the absorption of energy. For the energy absorption, a bolt is disposed on the retaining part which projects into an elongated hole of an energy absorption part disposed on the jacket unit and which, during its shift in the event of a crash, widens this elongated hole. To attain defined energy absorption, the material properties of the energy absorption part in the proximity of the elongated hole must be precisely defined such that they are reproducible.
Similar steering columns are also disclosed in EP 0 849 141 A1 and EP 1 464 560 A2. The retaining parts are guided by guide parts in the manner of a carriage such that they are displaceable in the longitudinal direction of the steering column. They are held under frictional closure with respect to the guide parts or plastically deform them with the consumption of energy. In the case of a frictionally engaged mounting, the clamping force of the securement device must be taken into account when considering the magnitude of the energy absorption. In a plastic deformation of the guide parts, their material properties must be implemented in a precisely defined reproducible manner.
A steering column of the above type is disclosed in DE 10 2008 034 807 B3. The retaining part is connected with the jacket unit, for one, across a bending wire or strip and, for another, across a pin forming a break-away connection between the retaining part and the jacket unit. If, in the event of a crash, a force, acting onto the steering wheel-side end of the steering shaft parallel to the longitudinal axis of the steering shaft in the direction towards the vehicle front, exceeds a limit value, the pin is shorn off and the break-away connection is consequently released. The jacket unit can then become dislocated with respect to the retaining part parallel to the longitudinal axis of the steering shaft in the direction toward the vehicle front, wherein the bending wire or strip is deformed and thereby energy is absorbed. The retaining part is herein hindered from being displaced in the direction parallel to the longitudinal axis of the steering shaft through its engagement with its securement part of the securement device. In the opened state of the securement device, the securement part is raised from the retaining part and the jacket unit, together with the retaining part, can be displaced parallel to the longitudinal axis of the steering shaft in order to carry out a length positioning of the steering column. Further, in the opened state of the securement device, a height or inclination adjustment of the steering column is feasible.
One disadvantage in this prior known steering column includes that during the opening of the break-away connection a force peak (=break-away peak) occurs, e.g. the limit value of the force acting parallel to the longitudinal axis of the steering shaft, starting at which the break-away connection is released and an energy absorbing displacement of the jacket unit with respect to the retaining part sets in, is relatively high. After the break-away connection has been released, the force counteracting a displacement of the jacket unit with respect to the retaining part is less.